1. Field of the Invention
The present invention relates to an antenna arrangement including a phased array which has a fixed phase taper along one axis across the face of the array and a selective phase taper along a second orthogonal axis across the face of the array to provide a beam which is squinted at an angle 90 degrees-.alpha. including signals with a first polarization direction. A single properly inclined polarization rotator or two properly inclined polarization rotators are provided in the path between the array and a polarization diplexer depending on the direction of polarization and whether the array is a linear or a two-dimensional array to provide the polarization matching at the array.
2. Description of the Prior Art
With high capacity satellite communication systems as with subscription program satellite systems vendors or users, ground stations may wish to communicate with two or more satellites positioned at different locations along the Geosynchronous Equatorial Arc (GEA). At present, a separate ground station antenna would be used to communicate with each satellite of the system making ground stations more complex and costly. A single antenna that can track, or simultaneously or sequentially communicate with, all satellites of interest could circumvent the above problems.
Movable antennas, which are well known in the art, could be used for tracking purposes or for communicating with one or more satellites, but such type of antennas are not useful when fast switching between multiple satellites is required. Multibeam reflector antennas using separate feedhorns are also well known in the art and have been suggested for satellite ground stations. In such antennas, oversized reflectors may be required while the scanning capability of others may be limited by excessive gain loss. With some of the specially designed and aberration correcting multireflector antennas with multiple feeds, for example, for a 0.5 degree beamwidth and 45 degrees of GEA coverage, a .+-.45 beamwidth scan capability is required. Such severe requirement introduces an antenna gain loss of 1 dB or more due to phase aberrations, as well as imposing a cumbersome antenna structure.
In the abstract "Narrow Multibeam Satellite Ground Station Antenna Employing a Linear Array with a Geosynchronous Arc Coverage of 60.degree." by N. Amitay et al in 1981 International Symposium on Antennas and Propagation, Vol. II, June 16-19, 1981, Los Angeles, Calif. at page 465, a multibeam array antenna including a linear array with properly phased elements is suggested which can be made to accurately track a 60 degree segment of the geosynchronous equatorial arc by scanning other than in cardinal planes of the array.
The problem remaining in the prior art is to provide an antenna capable of scanning a wide angle of a predetermined arc in the far field of the antenna using a linear scan of a beam including orthogonally polarized signals while substantially eliminating polarization mismatch at any array caused by a polarization diplexer when scanning is performed outside the cardinal planes of an array since polarizations do not remain orthogonal in such arrangement.